CONSTRUCTED WETLAND IN RIVER WATER QUALITY IMPROVEMENT
Abstract:A pilot-scale wetland was constructed next to the bank of a discharge to study the feasibility of water quality improvement. The wetland is 25 m long and 6 m wide with impermeable underlay, has two parallel channels. Each channel (1.98 m wide on top, 0.45 m at bottom, and 0.5 m high) was packed with rocks and had working volume of 19.2 m3 and porosity of 0.457. This subsurface flow system was operated for two dry seasons from Nov., 1998 to May, 1999 and Nov., 1999 to May, 2000.
Two channels received identical flow rate except that different plants might grow on each channel. Flow rates tested were from 1.7 to 127.6 m3/d in each channel, and this gave hydraulic retention times (HRTs) of 120 to 1.6 hours. Organic loading rates (OLRs) ranged from 0.002 to 0.219 kg TCOD/m3-d. Results indicated that removal rates of suspended solids (SS) ranged from 53.1–63.5%, with similar results for volatile SS (55.3 to 58.5%). This means physical filtration was the predominant removal mechanism. Removal rates of total COD (Chemical Oxygen Demand) in both channels were similar (37.9–38.7%). That soluble COD was not removed as effectively as total COD suggested physical filtration was more significant than biological transformation in the wetland. Higher BOD (Biochemical Oxygen Demand) removal rates than total COD or soluble COD indicated some CODs were not quite biodegradable. Experiences in operation and maintenance of constructed wetland concluded that a design of backwash was necessary, and frequent harvest of plants was necessary in order to achieve better nitrogen and phosphorus removal rates.
Document Type: Research Article
Publication date: January 1, 2000
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